Due to the density of modern magnetic data storage media, magnetic data storage media requires servo tracks be printed onto the media to minimize data-track registration errors. The servo tracks are often written onto the storage media in the media production facility, where it is necessary, after writing servo tracks or patterns, to verify that the tracks have been properly printed onto the media and meet the production specifications. This verification process is accomplished by running a servo verify magnetic recording head, e.g. read head, over the media on which the servo tracks are printed.
A servo head, in this case particularly a servo verify head, generally requires an ensemble of magnetic structures. Standard processing techniques and tools for assembling magnetic structures generally operate in an orthonormal coordinate system. Thus, the processing of magnetic structures at an angle to the standard processing planes poses unique challenges.
In the magnetic data storage media industry, there are many methods of writing or implementing magnetic servo tracks on storage media. Servo tracks have many different geometries. One specific method and geometry is that of timing based servo (TBS). TBS utilizes successive magnetic transitions written on the media at non-orthogonal angles with respect to the travel direction of the media (e.g. tape). FIG. 2a illustrates this method. Two separate servo bands 42 are shown, with a set of four magnetic patterns or tracks 40a and 40b at +6° and −6° respectively.
The uniqueness of TBS patterns is due to magnetic structures at an angle to standard processing planes, i.e. non-orthogonal angles with respect to the travel direction of media. To verify TBS patterns or tracks on the media, it is desired that the magnetic sensing regions (read gap) on a servo verify head are effectively parallel to the corresponding magnetic transitions (servo patterns) printed on the media. Non-parallelism between the magnetic transition on the tape and the magnetic read head may lead to detection inefficiencies and lower sensitivity of the resultant signals through azimuth loss.
One method for verifying a TBS pattern is to sense or read a full servo transition at once, a so-called full-band verify. With this method, the full pattern width of any single transition is detected at once. With full-band verify, it is desirable to have good azimuth alignment between the magnetic head read gap and the servo transition on tape. Misalignment between these will cause the magnetic transition to be effectively smeared across the read sensor, causing detection efficiency and sensing accuracy loss. Severe azimuth misalignment, may even cause more than one magnetic transition to be intersecting the read sensor (gap) simultaneously, confusing what transition was verified.
Another method for verifying a TBS pattern is the so-called partial-band verify. With this method, a narrow read gap magnetic head is used. If the read gap width is sufficiently small relative to the TBS pattern width, the amount of azimuth misalignment acceptable is eased. In one example, a TBS pattern with a width of 190 μm at an angle of 6° can be verified by a read sensor with a width of 5-10 μm at an azimuth angle of 0°. This method allows the production of a servo verify head without the complexity of processing previously mentioned. This method also requires that the servo verify head be mechanically scanned along the TBS pattern transition width to sample the full servo pattern. Both the above mentioned methods have advantages and disadvantages and are practiced in the industry.
One advantage of the full-band verify method is that the head is stationary, eliminating the need for a scanning actuator to move the head in the cross-track direction. Another advantage of the full-band verify method is that the entire width of each pattern in the servo band is verified. On the other hand, it may be difficult for the full-band verify method to detect small localized defects in the servo pattern. In one example, a localized defect of 5 μm along a 190 μm track width, which is repeated down the servo band, may not be properly detected.
One advantage of the partial-verify method is that the repeatable small local defects previously mentioned can be intersected and properly detected as the head scans back and forth. In a partial-verify method, however, an appropriate scan rate, i.e., how long it takes to scan the width of a servo band, may be desired in representing the fraction of any servo pattern sampled. Large temporary defects where a significant portion of a servo pattern is missing, and where the defects only repeat for a small number of servo patterns, may not be intersected by the scanning head and hence be undetected. Hence, it is desirable to detect these defects with an appropriate scan rate and in an efficient and capable manner in the production facility.
Also, in the processing of magnetic structures of a servo head for verifying TBS patterns, independent channels at a specified angle are desired. This allows each servo pattern and any defects of that servo pattern to be detected independent of any other servo pattern.
Further, in the processing of magnetic structures of a servo head for verifying TBS patterns, it is desirable to assemble or bond independent cores while maintaining multi-dimensional tolerances.
An additional feature of a magnetic servo verify head is a proper head to tape interface. If the head to tape interface is poor, the tape may not contact the head appropriately, leading to sensing inefficiency. A magnetic head surface generally requires an appropriate geometry to obtain a good or acceptable head to tape interface. One standard geometry for a magnetic servo head used in the industry is a cylindrical contour. As an example, typical cylindrical contours may have a radius from 5 mm to 25 mm. A cylindrical contour generally limits the length of the head (down-tape or down-track direction) to achieve a good interface. Therefore, the spatial location acceptable for magnetic elements on a cylindrical contour is restricted.
Thus, depending on the desirable geometry and form factor of a magnetic servo head surface, TBS patterns may add a high degree of complexity to processing techniques of the ensemble of magnetic structures for a servo verify head.
Therefore, there is a need for a servo head to verify TBS patterns printed on data storage media, and further there is a need for a method of assembling a servo head having acceptable head geometry and form factor of a servo head surface to be adapted for verifying TBS patterns.